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Tropical Storm Leslie Forecast Discussion Number 50
2018-10-08 22:48:22| National Hurricane Center (Atlantic)
Issued at 500 PM AST Mon Oct 08 2018 000 WTNT43 KNHC 082048 TCDAT3 Tropical Storm Leslie Discussion Number 50 NWS National Hurricane Center Miami FL AL132018 500 PM AST Mon Oct 08 2018 GOES-16 data indicate that Leslie has a small central dense overcast with an inner core trying to form on the last few visible images. Convection has also deepened somewhat, and the overall cloud pattern is becoming more symmetric. All signs point to strengthening and the Dvorak estimates are increasing. So for Leslie's 50th advisory, the wind speed is raised to 50 kt, near the CIMSS ADT value. Leslie is moving southeastward at about 12 kt; an unusually fast pace for this direction. The storm is forecast to slow down somewhat and turn toward the south-southeast during the next day or two as the cyclone separates from the mid-latitude flow temporarily and becomes steered by a mid-level ridge over the central Atlantic. Fortunately the ridge isn't strong enough for Leslie to move westward again, and the models all eject Leslie northeastward because of a deepening trough over the eastern Atlantic. There has been a notable trend southward through 48 hours, and the official forecast follows that idea. The forecast becomes a nightmare at long range, however, with very little agreement on whether Leslie is accelerated ahead of the trough, like the latest FV3GFS, or gets left behind again, like the ECMWF. These differences result in a 1200 mile spread of the historically reliable models by day 5, resulting in a very low confidence forecast. The bulk of the guidance is now indicating that the "left behind" option is becoming more likely, but continuity dictates making forecast changes in smaller chunks. So the official forecast is much slower and farther south at long range, but is well north of the latest model consensus. Further southward adjustments could be required if model trends continue. Interestingly, model guidance is becoming more certain on Leslie becoming a hurricane again as it moves over warmer (but still marginally warm) waters, into a lighter-shear and higher mid-level humidity enviroment. This makes some sense given that the track is shifting southward and Leslie should finally move over a warmer portion of the subtropical Atlantic that it hasn't touched yet. Thus the intensity forecast is higher than the previous one, and the corrected-consensus models even suggest category 2 as a peak intensity is possible. By day 5, increasing shear and cooler waters should weaken Leslie, and it could be undergoing extratropical transition at that time. FORECAST POSITIONS AND MAX WINDS INIT 08/2100Z 33.8N 45.8W 50 KT 60 MPH 12H 09/0600Z 32.5N 44.4W 55 KT 65 MPH 24H 09/1800Z 30.6N 43.2W 55 KT 65 MPH 36H 10/0600Z 28.9N 42.5W 60 KT 70 MPH 48H 10/1800Z 28.2N 41.7W 65 KT 75 MPH 72H 11/1800Z 29.5N 37.0W 75 KT 85 MPH 96H 12/1800Z 33.5N 26.5W 75 KT 85 MPH 120H 13/1800Z 37.0N 17.0W 60 KT 70 MPH $$ Forecaster Blake
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